Protection of parallel transmission-lines.



N0. 848,92. PATENTED APR. 2, 1907.

, A. FJARE.

PROTECTION OF PARALLEL TRANSMISSION LINES.

APPLICATION FILED 00117. 1904.

Witnesses. lnve'fitor.

W finders F jar e.

byWUM q- Atty THE :loRms FXETERS '10. WASHINGTON, D. cv

UNITED STATES PATENT OFFICE.

ANDERS FJARE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A GORPORATION OF NEW YORK.

Specification of Letters Patent.

Patented April 2, 1907.

Application filed October 17, 1904:. Serial No. 228,674.

T0 on whom it may concern:

Be it known that I, ANDERS FJARE, a subject of the King of Norway, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Protection of Parallel Transmission-Lines, of which the following is a specification.

My invention relates to the protection of parallel transmission-lines or feeders; and its object is to provide simple, efficient, and reliable means for opening the circuit of any one of the transmission-lines or feeders when a short circuit occurs thereon without intere rupting the circuits of the other feeders or in any way interfering with the supply of current to the load at the receiving end.

Where a plurality of transmission-lines or feeders are connected in parallel at both ends, it is not sufficient to open the circuit of a feeder at the generator end alone when a short circuit occurs upon it, since as it is connected to the other feeders at the receiving end the other feeders will supply current which will flow back through the faulty feeder from the receiving end to the fault. Various devices have been proposed here tofore having for their object the cutting out of a faulty feeder at the receiving end upon a reversal of current-flow relative to the current in the other feeder. Many of these devices depend for operation upon the use of a potential transformer the secondary current from which acts with the secondary current from a series transformer to operate a switch in the circuit of a feeder. All such devices are open to the objection that upon a short circuit of very low resistance the potential may be so lowered as to render the devices inoperative, and consequently they are liable to failure at the time when operation is most required. Furthermore, with hightension lines potential transformers are expensive pieces of apparatus.

By my invention the necessity for potential transformers is eliminated and only series transformers are employed, while at the same time a discriminating action of the protective devices is obtained, so that only the faulty feeder is cut out.

My invention will best be understood by reference to the accompanying drawing, which shows diagrammatically the receiving ends of four parallel feeders or transmissionlines provided with protective devices .in accordance with my invention.

In the drawing, A, A A and A repre sent four three-phase transmission-lines connected to the receiving bus-bars B through the respective switches S, S S and S The switch S is provided with a trippingcoil 0, one terminal of which is connected to the conductor 1 and the other arranged to be connected to the conductor 2 through either of the relays R. A battery 6 is connected across the conductors 1 2. Thus it is evident that when either relay R is closed the tripping-coil 0 will be energized and the switch S opened, disconnecting the line A from the bus-bars. The other switches are provided with similar tripping-coils similarly arranged.

Two of the three phases of the line A are each provided with two series transformers t t and t t*. The secondary of the series transformer t has one terminal grounded and the other terminal connected, through one coil of the left-hand relay R, to the conductor 3, which is also groundedthat is, the secondary of this transformer t is shortcircuited through one coil of the relay R. The second series transformer t in the same phase has one terminal of its secondary grounded and the other terminal connected, through one primary coil 6 of transformer T, to conductor 4:, which is also grounded that is, the secondary of transformer t is short cirouited through primary coil 6. Similarly it will be seen by tracing out the circuits that the transformer 25 has its secondary short-cirouited through one coil of the right-hand relay R, while the transformer t has its secondary short-cirouited through the primary coil e of transformer T The other transmission-lines are provided with series transformers similarly arranged and connected. Consequently transformer T is en ergized by currents derived from the same phase of all four transmission-lines, while transformer T is similarly energized from the currents of a second phase of all four lines. Each of the transformers T and T is provided with four secondary windings.

The secondary winding f of transformer T is short-cirouited through the second coil of the left-hand relay R. The secondaryf is similarly short-cirouited through a coil on the left-hand relay R &c. The secondary f 5 of IOO transformer T is short-circuited through one of the coils of right-hand relay R. ondary f of the same transformer is shortcircuited through a winding of the right-hand relay R, &c. Thus it will be seen that each relay is energized by a current derived from one phase of one line, while its other coil is ianergized from current derived from all four mes.

The transformers are so wound and connected that the currents through the two windings of each relay are normally equal and opposite, and consequently all the relays remain open during normal operation of the system. When, however, one of the transmission-lines becomes short-circuited, the current in that line will be reversed relative to the currents in the other lines. Thus, for instance, if the transmission-line A becomes shortcircuited the current in two or more of its phases will be reversed relative to the currents in the corresponding phases of the other lines, and consequently the currents in one or both of the relay-coils energized from transformers t and 25 will be relatively reversed. The other coil of the relay, which is energized by currents derived from all four lines, will not have the direction of its current-flow relatively reversed, but will be traversed by a current having a magnitude depending upon the amount of current in the secondary of transformer t compared with the sum of the currents in transformers t, Z and or in the secondary of transformer i compared with the sum of the currents in the secondary of transformers 25 25 and 19, according as to which phase is reversed. Obviously if there is no load on the bus-bars B, so that all the current in the other three transmission-lines flows back through the transmission-line A, and if the several series transformers are designed with cores of such proportions as to remain unsaturated with ordinary current-flow the current in the secondary of transformer t that is, if that is one of the phases of line A shorteircuitedwill be equal and opposite to the sum of the currents in the transformers t, t, and 15. In that case the primary winding 6 would balance the three other windings, and the current in the same winding of relay R, which is derived from the sum of these currents, would be zero, and the first current alone would act to open the relay. Similarly the other relays R R and B would also have one coil no longer traversed by a current, while the other coil would be traversed by a current equal to one-third of the current in the secondary of transformer t. WVhile this arrangement would be operative with the particular type of relay shown, if provided with time-limit devices, since the pull upon the relay R would be three times as great as that upon the others, nevertheless in order to make the action more reliable and positive and in order to make it possible to The sec use other types of relay, if desired, requiring the joint action of two currents, I prefer to make the several series transformers with cores proportioned to be saturated by. a fraction of the normal full-load current. This being the case, the current in the secondary of transformer 25 is no longer three times as great as that in the secondary of transformer i when the line A is short-circuited, but is approximately equal thereto. Consequently the primary winding 6 no longer balances the other three primary windings, but merely neutralizes the effect of one of them, so that the relay-coils energized from the several secondaries of the transformer T are traversed by currents in the same relative directions as before, but partly reduced in strength. Consequently in the relay R both currents are in the same relative direction and assist each other in moving the core, while the currents of the two windings of the other relays are still opposed, so that there is little or no tendency for these relays to close.

hile I have illustrated my invention as applied to the protection of four three-phase lines, it will be understood that my invention is not limited to this particular number, but is applicable to any number of lines greater than two or any number of phases. Any well-known type of reverse-current relay may be employed in place of that shown. Accordingly I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invention.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1.. The combination with three or more parallel transmission-lines, two series transformers for each line, a differential tripping device for each line, means for producing in each tripping device two opposing forces proportional respectively to the secondary current of one series transformer for that line and to the algebraic sum of the secondary currents in the other transformer and the corresponding transformers of the other lines, and a switch in the circuit of each line controlledby the tripping device for that line.

2. In combination with three or more parallel transmissionlines, two series transformers for each line, a differential tripping device for each line having one winding con nected to the secondary of one of said transformers for that line and a second winding energized. with a current proportional to the algebraic sum of the secondary currents of the series transformers of the corresponding phase of all said lines, and a switch in the circuit of each line controlled by the tripping device for the line.

3. In combination with three or more parallel transmission-lines, two series transformers for each line, a transformer energized in common from series transformers in all the lines, a differential tripping device for each line having one winding connected to the secondary of one of the series transformers in that line and the other connected to a secondary of the common transformer, and. a switch in the circuit of each line controlled by the tripping device for that line.

4. In combination with three or more parallel transmission-lines, two series transformers in each line, a differential tripping device for each line, a transformer having a plurality of primary coils severally connected to the secondaries of one of the series transformers in each line, a differential tripping device for each line having one winding connected to the secondary of the other of the series transformers in that line and the other winding connected to a secondary winding on the common transformer, and a switch in the circuit of each line controlled by the tripping device for that line.

5. In combination with three or more parallel transmission-lines, two series transformers for each line having cores adapted to be saturated by a fraction of the full-load current of the line, a differential tripping device for each line, means for producing in each l tripping device two opposing forces proportioned respectively to the secondary current of one series transformer for that line and to the algebraic sum of the secondary currents in the other transformer and the corresponding transformers of the other lines, and a switch in the circuit of each line controlled by the tripping device for that line.

6. In combination with three or more parallel transmission-lines, two series transformers in each line having cores adapted to be saturated by a fraction of the full-load current of the line, a transformer having a plurality of primary coils severally connected to the secondaries of one of the series transformers in each line, a differential tripping device for each line having one winding connected to the secondary of the other of the series transformers in that line and the other winding connected to a secondary winding of the common transformer, and a switch in the circuit of each line controlled by the tripping device for that line.

In witness whereof I have hereunto set my hand this 15th day of October, 1904.

' ANDERS FJARE.

Witnesses:

JAMEs O. CARR, HELEN Onronn. 

